Sulphydryl acid and imidazoline salts as inhibitors of carbon corrosion of iron and ferrous metals

ABSTRACT

The invention concerns inhibitor compositions based on fatty sulphydryl acid and poly(ethyleneamino)imidazoline salts for considerably reducing the corrosive effect of carbon brine on iron and ferrous metals. These compositions are as efficient when the corrosive medium is driven with a high flowrate and in biphasic brine/oil medium.

TECHNICAL FIELD

The invention relates to the inhibition of corrosion of iron and offerrous metals in carbonic brines. For the purposes of the invention,the term carbonic brines is understood to refer to carbondioxide-charged aqueous solutions of inorganic salts.

BACKGROUND ART

(C₁₀-C₂₂)Alkyl-poly(ethyleneamino)imidazolines (or 2-alkylpoly-3-(ethyleneamino)-1,3-diazolines) are known to be excellentcorrosion inhibitors for iron and ferrous metals in sulphydric brines,or sulphydric and carbonic brines, and many publications have beendevoted to the mechanism of this inhibition. To mention but the mostrecent: Preparation of Corrosion Inhibitor for Water Flooding inOilfield and Study of its Mechanism, Lu Zhu et al., Water Treatments, 8(1993), 253-264, China Ocean Press or Hydrogen Sulphide Corrosion ofSteel, Mechanism of Action of Imidazoline Inhibitors, A. J. Szyprowski,Proceedings of the 8th European Symposium on Corrosion Inhibitors, Ann.Univ. Ferrara, N. S., Sez. V, suppl. N.10, 1995. However, curiously,these compounds are very ineffective in corrosive media containing onlyCO₂, which are nevertheless apparently less aggressive, and thismotivated the search for more complex similar structures such asN,N′-substituted imidazolines (U.S. Pat. No. 5,322,640) or adducts ofimidazolinones and of urea (GB2,190,670).

DISCLOSURE OF INVENTION

It has now been found that salts of mercapto acids and ofalkyl-polyethyleneamino-imidazolines are very powerful corrosioninhibitors for iron and ferrous metals in carbon dioxide-charged aqueoussolutions of inorganic salts.

The present invention consists of corrosion-inhibiting compositionscontaining at least one alkyl-poly(ethyleneamino)-imidazoline or2-alkyl-poly-3-(ethyleneamino)-1,3-diazoline, corresponding to thegeneral formula

in which R is a linear or branched, saturated or unsaturated hydrocarbonchain containing 10 to 22 carbon atoms, and in which n is a number from0 to 3, and at least one mercapto acid corresponding to the generalformula

with

n=0 to 3,

R₁=H or SH,

R₂ and R₃, together or independently, =C₁₋₄, CON(R₆)(R₇) or COOR₈,

R₄ and R₅, together or independently, =OH, NH₂ or SH when R₁≠SH,

R₆ and R₇, together or independently, =H or C₁₋₄,

R₈=H or C₁₋₈,

it being possible for R₂ to R₅ to be included in an aliphatic ring,

it being possible for R₃ and R₅ to be included in an aromatic ring whenn=1,

A being a COOH, SO₃H, OSO₃H, PO₃H or OPO₃H acid group,

the molar ratio between the mercapto acid component(s) and theimidazoline component(s) being from 1.0 to 1.5.

The alkylimidazolines forming part of the composition of the inhibitorsof the invention are products of condensation-cyclization of saturatedor unsaturated fatty acids containing 10-22 carbon atoms, withpolyethylene-polyamines (diethylenetriamine DETA and its higherhomologues, triethylenetetramine TETA, tetraethylenepentamine TEPA andpentaethylenehexamine PEHA). These imidazolines are obtained underconditions that are well known to those skilled in the art (introductionof the polyamine into the molten fatty acid, in the presence of oxalicacid which acts as cyclization accelerator, raising the temperature to200° C.-220° C. and maintaining it at this stage until the water ofcondensation has been entirely removed).

The preferred mercapto acids are mercaptocarboxylic acids,

HS—(CH₂)_(n)—COOH

and among these mercaptoacetic acid,

HS—CH₂—COOH

and mercaptopropionic acid

HS—CH₂—CH₂—COOH.

The compositions according to the invention are advantageously in theform of aqueous solutions containing 10%-75% active material. Solutionscontaining 20-40% by weight in water or in a mixture of water and awater-miscible solvent are preferred, isobutanol, butyl glycol,monoethylene glycol or mixtures thereof being preferred solvents. Theyare prepared very simply by mixing the constituents together while coldor warm. They are used at effective concentrations of 5 to 200 ppm,preferably at about 20 ppm of the preparation (calculated as imidazolinemercaptocarboxylate component relative to the corrosive medium).

These water-soluble compositions, modelled on the traditional butinsufficiently effective imidazoline acetates, inhibit the staticcorrosion of iron and ferrous metals in carbonic brines of high salinityat high temperature. They also inhibit its dynamic corrosion under theconditions for the production of gas, and their efficacy is maintainedin two-phase media such as carbonic brines/oils. However, in order toenhance their performance when the hydrocarbon phase is a crudepetroleum oil and when the aqueous phase is highly saline, i.e. when itssalt concentration is greater than 1 g/l, they are advantageouslycombined with cationic, amphoteric and nonionic surfactants from thegroup consisting of alkyltrimethyl- or alkyldimethylbenzylammoniumsalts, alkylaminopropionic acids and oxyethylenated alkylamines, inwhich the alkyl chain is a saturated or unsaturated chain containingfrom 12 to 22 carbon atoms. This effect is unexpected; it is notimpossible for it to be due to the improvement to the partition of themercaptocarboxylate/imidazoline system between the oily phase and theaqueous phase.

The mercaptocarboxylate/imidazoline/surfactant compositions typicallycomprising 20 to 40% imidazoline mercaptocarboxylate, 2 to 5% quaternaryammonium, 2 to 5% amphoteric surfactant and 2 to 10% oxyethylenatedamine are also subjects of the present invention.

The examples which follow will allow a better understanding of theinvention to be gained.

EXAMPLES Example 1

Preparation of Mercapto Acid/Imidazoline Inhibitory Compositions

Various imidazolines are prepared by condensing 1 mol of fatty acid with1.15 mol of tetraethylenepentamine (TEPA) in the presence of 1% byweight of oxalic acid dihydrate. The amine is introduced into the fattyacid-oxalic acid mixture at a temperature of 140° C., after which thereaction mixture is brought to 160° C. and maintained at thistemperature for 1 h 30, then brought to 200° C.-220° C. for 16 h. Theinhibitory compositions consist of imidazolines (30% by weight),thioglycolic acid (5% by weight) and isobutanol (65% by weight). Thecorresponding controls consist of imidazolines, glacial acetic acid andisobutanol in the same proportions.

The inhibitory compositions I1, I2, I3 and I4, respectively, are thusprepared with imidazolines obtained from tall-oil, from coconut fattyacid, from oleic fatty acid and from rapeseed oil, and the correspondingcontrol compositions T1 to T4 (acetic) are prepared.

All of these compositions are homogeneous liquids of oily appearance.

Example 2

Measurements of static corrosion are carried out in a medium consistingof an aqueous solution containing, in grams per liter:

NaCl 277.50 KCl 6.43 CaCl₂.2H₂O 21.50 MgCl₂.6H₂O 33.77 BaCl₂.2H₂O 0.20SrCl₂.2H₂O 0.34 FeCl₂ 0.06

This medium is de-aerated beforehand with nitrogen and then saturatedwith CO₂. Its pH is 5.5.

The corrosion test is carried out on a test piece of 1 cm² XC18 steel,in a device for measuring polarization resistance, the corrosive mediumbeing at 80° C., the CO₂ pressure being 1 bar. The results are reportedin the table below, in which they are expressed, as is traditional, as apercentage of protection.

PERCENTAGE OF PROTECTION Formulae Control formulae according to the(acetic) invention (thioglycolic) doses ppm T1 T2 T3 T4 I1 I2 I3 I4  1˜0 ˜0 ˜0 ˜0 ˜0 ˜0  8  7  7 ˜0 ˜0 ˜0 ˜0 17 25 16 22  5 ˜0 ˜0 ˜0 ˜0 64 6071 69  10 ˜0 ˜0 ˜0 ˜0 81 82 83 86  20 ˜0 ˜0 ˜0 ˜0 84 89 85 87  50 ˜0 ˜0˜0 ˜0 85 90 84 90 100 ˜0 ˜0 ˜0 ˜0 86 92 83 92 200 18 ˜0 ˜0 ˜0 86 94 8894

These results unequivocally reflect the efficacy of theimidazoline/thioglycolic acid compositions according to the invention.

Example 3

Test of Dynamic Corrosion

The test simulates the conditions of gas production. The corrosivemedium consists of an aqueous solution of NaCl at 1 g/l, de-aeratedbeforehand with nitrogen and then saturated with CO₂, brought to 60° C.and circulating at a speed of 13 meters per second in a so-called “JetImpingement” device (see: Correlation of Steel Corrosion in Pipe Flowwith Jet Impingement and Rotating Cylinder Test, K. D. Efird et al.,Corrosion, vol. 49, No. 12, p. 992, 1993). The test body subjected tocorrosion under these conditions is a test piece of XC18 steel in theshape of a ring 1 mm in thickness and with an internal radius of 2.5 mm,whose rate of corrosion is measured by polarization resistance.

FIG. 1 reproduces the results obtained from a blank test (free ofinhibitor) and in the presence of compositions T4 and I4 (formulationsbased on rapeseed imidazoline acetate and thioglycolate respectively).The inhibitory compositions were used at a dose of 20 ppm (expressed asvolumes of preparation relative to the corrosive medium). These resultsunambiguously bear witness to the efficacy of the inhibitor according tothe invention under the conditions of corrosion by carbonic brineanimated with a high flow rate.

Example 4

Test of Corrosion in a Two-phase Medium

The corrosive medium is a mixed phase consisting of 90% by volume of anaqueous solution of sodium chloride at 1 g/l and 10% paraffin oil. Thesystem is de-aerated beforehand by bubbling nitrogen through, and isthen saturated with CO₂. The working temperature is 60° C. Homogeneityof the medium is ensured in the assembly by means of gentle magneticstirring.

The corrosion inhibitor used is composition I4 (based on rapeseedimidazoline). It is used at a dose of 20 ppm (calculated as volume ofinhibitory preparation relative to the total volume of the corrosivemedium). The rate of corrosion is estimated, as in the previousexamples, by polarization resistance, in a test procedure summarizedbelow.

Rate of corrosion in the aqueous phase Conditions (in mm/year) A.Precorrosion in aqueous phase  1.5 mm/year after precorrosion for 12hours B. Introduction of the oil  1.4 mm/year after 2 hours ofstabilization C. Introduction of the inhibitor via the oil 0.002 mm/yearphase after 12 hours of stabilization

Example 5

Crude Petroleum/Very Saline Brine Two-phase Medium

The corrosion test is carried out in a corrosive medium consisting of10% of a crude petroleum oil from the Gabon taken at the site, and 90%reconstituted site water with the following composition:

SrCl₂.6H₂O 0.34 g/l BaCl₂.2H₂O 0.2 g/l MgCl₂.6H₂O 33.77 g/l KCl 6.43 g/lCaCl₂.2H₂O 21.5 g/l FeCl₂.4H₂O 0.06 g/l NaCl 277.5 g/l

At the time of the test, 1.8 g/l of acetic acid are added and themixture is acidified by a strong acid (HCI) in order to reach a pH of5.5. It is de-aerated with nitrogen for one hour and then saturated withCO₂ for one hour. 0.05 g/l of NaHCO₃ is added, bubbling of CO₂ iscommenced and the temperature is raised to 80° C., which takes about ½hour.

The rate of corrosion of the steel in the brine is measured bypolarization resistance, a measurement being repeated every ¼ hour forone hour. Crude Gabon petroleum oil (10% relative to the brine)presaturated with CO₂ and brought to 80° is then added, and monitoringof the rate of corrosion is continued by measuring the polarizationresistance every ¼ hour for a further one hour. 20 ppm of corrosioninhibitor (as imidazoline mercaptocarboxylate) are then added and thechange in the rate of corrosion is monitored by measuring thepolarization resistance, this being carried out every ¼ hour for fourhours.

A simple inhibitory composition consisting (as a per cent by weight) of:

Imidazoline 25 Mercaptoacetic acid  5 Butyl glycol 25 Monoethyleneglycol 25 Water 20

is compared with an inhibitory composition improved by addingsurfactants as mentioned above, consisting (as a per cent by weight) of:

Imidazoline 20 Mercaptopropionic acid  5 Monopropylene glycol 60 Coconutdimethylbenzylammonium  5% chloride at 50% Coconut monoamine with 11 mol 5% of ethylene oxide Coconut aminopropionic acid at 60%  5%

In these compositions, the imidazoline is that of Example 1. The coconutdimethylbenzylammonium chloride used is Noramium® DA50 from CECA S.A.,which is presented at a concentration of 50% active material, theoxyethylenated coconut monoamine is the oxyethylenated productcontaining on average 11 mol of ethylene oxide, sold by CECA S.A. underthe name Noramox® C11, and the coconut aminopropionic acid is Amphoram®CP1 from CECA S.A., which is presented for sale at a concentration of60% active material.

The changes in the rate of corrosion as a function of time in thepresence of 20 ppm of the first formulation and of the secondformulation, respectively, are represented in FIG. 2. It is observedthat the values of the residual rate of corrosion after contact for 8hours 30 become established at 0.60 mm/year and 0.035 mm/yearrespectively, which bears witness to the real efficacy of the secondformulation under the test conditions.

What is claimed is:
 1. Compositions for inhibiting the corrosion of iron and ferrous metals in carbonic brines, comprising, as active constituent, at least one alkyl-poly(ethyleneamino)-imidazoline or 2-alkyl-poly-3-(ethyleneamino)-1,3-diazoline, corresponding to the general formula

in which R is a linear or branched, saturated or unsaturated hydrocarbon chain containing 10 to 22 carbon atoms, and in which n is a number from 0 to 3, and at least one mercapto acid corresponding to the general formula

with n=0 to 3, R₁=H or SH, R₂ and R₃, together or independently, =C₁₋₄, CON(R₆)(R₇) or COOR₈, R₄ and R₅, together or independently, =OH, NH₂ or SH when R₁≠SH, R₆ and R₇, together or independently, =H or C₁₋₄, R₈=H or C₁₋₈, it being possible for R₂ to R₅ to be included in an aliphatic ring, it being possible for R₃ and R₅ to be included in an aromatic ring when n=1, A being a COOH, SO₃H, OSO₃H, PO₃H or OPO₃H acid group, the molar ratio between the mercapto acid component(s) and the imidazoline component(s) being from 1.0 to 1.5.
 2. Inhibitory compositions according to claim 1, wherein the mercapto acid is a mercaptocarboxylic acid.
 3. Inhibitory compositions according to claim 1, wherein the mercapto acid is mercaptoacetic acid or mercaptopropionic acid.
 4. Inhibitory compositions according to claim 1, further comprising, besides mercapto acids and 2-alkyl-poly(3-ethyleneamino)-1,3-diazolines, at least one cationic surfactant of the alkyltrimethyl- or alkyldimethylbenzylammonium salt type, an amphoteric surfactant of the alkylaminopropionic acid type and a nonionic surfactant of the oxyethylenated alkylamine type, wherein the alkyl chain is a saturated or unsaturated chain containing from 12 to 22 carbon atoms.
 5. Inhibitory compositions according to claim 4, further comprising from 20 to 40% imidazoline mercaptocarboxylates, 2 to 5% quaternary ammonium, 2 to 5% amphoteric surfactant and 2 to 10% oxyethylenated amine, dissolved in an aqueous or water-miscible solvent.
 6. Inhibitory compositions according to claim 5, wherein the water-miscible solvent is selected from the group consisting of isobutanol, butyl glycol, monoethylene glycol and a mixture of these solvents.
 7. Process for inhibiting corrosion of iron and ferrous metals in carbonic brines, in the presence or absence of oils, at rest or animated with a high flow rate, comprising introducing into a corrosive medium from 5 to 200 ppm, expressed as weight of inhibiting active principles, mercapto acids and alkylpoly(ethyleneamino)-imidazolines, relative to the volume of the corrosive medium, of the compositions of claim
 1. 